1. Field of the Invention
The invention relates to electrostatography and more particularly to a method and apparatus for applying a loading force to a roller used in image transfer.
2. Background of the Invention
In U.S. application Ser. No. 900,696 filed in the name of Tombs et al (the contents of which are incorporated herein by reference) there is disclosed an electrophotographic reproduction apparatus wherein a series of roller separation image forming stations are arranged so that a receiver sheet may be conveyed from station to station to receive color separation images in transfer so that the images are superposed onto each other to form a composite multicolor image. In the aforesaid application at each color separation station a compliant intermediate transfer drum or roller (ITR) has an electrically conductive core of for example aluminum, a relatively thick (1-20 mm) compliant blanket layer is around the core and a relatively thin (2 micrometers-30 micrometers) hard overcoat layer surrounds the blanket layer. The Young's modulus of the blanket layer is preferably between 0.1 MPa and 10 MPa, and the blanket layer has a bulk volume electrical resistivity preferably between 10.sup.7 -10.sup.11 ohm-cm. The Young's modulus of the overcoat layer is preferably greater than 100 MPa. The ITR forms a nip under pressure with a photoconductive (PC) drum. An electrical bias is impressed upon the ITR of suitable level and polarity to urge a developed toner image on the PC drum to transfer to the surface of the ITR. A receiver sheet is then moved into a second nip between the ITR and a paper transfer roller (PTR) in a timed or registered condition to receive the image in transfer from the ITR. An electrical bias of appropriate level and polarity is provided to the PTR to urge transfer of the toner image to the receiver sheet.
Heretofore, a PC drum and ITR were urged together by controlling the separation of their respective axes and establishing a predetermined interference in their respective radii of which interference is accommodated by the compliancy in the ITR blanket layer. However, this solution is not desirable because accommodation must be made when the machine is not producing prints to separate the PC drum from the ITR to avoid set forming in the ITR.
A further problem arises in attempting to load or unload relatively heavy rollers.
It is an object of the invention to provide a method and apparatus which provides for an improved manner of loading and for unloading a printing roller or drum assembly to or from the printing apparatus.